White, oriented polyester films are known.
DE-C-26 47 713 describes a photographic, biaxially oriented, opaque layer substrate which is comprised of a linear polyester and comprises, as sole particulate pigment, an amount of from 5 to 50% by weight of barium sulfate. The average grain size of the barium sulfate particles is from 0.5 to 10 μm. The photographic, biaxially oriented, opaque layer substrate features particularly high whiteness and particularly high opacity, without any discoloration of the layer substrate due to additives present therein during production. It also has low density, good specular gloss, and low overall light permeability. However, the film lacks adequate laser cuttability and laser inscribability using lasers in the visible or near-infrared region.
EP-A-1 322 719 describes a laser-cuttable multilayer material which comprises a crosslinking nitrogen-containing compound. These materials have very poor or no orientability and exhibit high levels of yellow discoloration on recycling, and are therefore not very suitable for industrial-scale production of biaxially oriented films.
White and transparent polyester films generally have good cuttability by CO2 lasers, which is to say that industrially useful cycle times are achieved in a usage example in which pieces of check-card dimensions are cut out from a film web. Markedly fewer cards per unit of time can be cut at conventional energy levels using the more familiar Nd:YAG lasers with wavelength around 1064 nm or frequency-doubled around 532 nm. Although white films have better laser-cuttability performance when compared with transparent polyester films, the cutting step is nevertheless often the rate-determining step in the process.